4cyl vs 3cyl

[leonz]

I have a B7800 ('03, purchased new) and I have never felt that it was too rough. Come on man, its a tractor not a Caddie! My 7800 has 400 hrs on it and has never failed to start nor had anything break (and it lives outside). I love this tractor. I agree with the others: get the tractor that can do the work you need (and then some just for "insurance").

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With the the three cylinder kubota engines in particular they are used for many other applications.


The nasty harmonics animal can create havoc at low rpm speeds if the engine isolation is poor especially with the hard( solid contact mounts on most of them.

The faster the low idle speed the greater force delivered to even the resonance between the prime mover (being the engine) and the tractor.

Using the 3 cylinder Duetz air cooled diesels as and example they are very civilized when mounted PROPERLY with the mounting feet and twin rubber pucks with steel spacers on all four corners.

When these yahoos put them in automobiles( CJ-5 jeeps) and expect to use motor mounts which are already there -thats another stupid move and the use of the rubber pucks is not possible and the normal balanced low idle which is what it was tested for at the factory and approved for with the fuel settings on the injection pump for the indirect injection engine in
which they occur with the rubber isolation mounts(been there done that (PROPERLY). The install was bad so the engine was blamed when it was the installer( outside shop that rube goldberged the entire thing.

Our boss buggies had the 3 cylinder water cooled engines in a modified kubota farm tractor- there was so much added weight because of the FOPS and 4 added seats and the rear tool carrier which was added it just absorbed it all at low idle.


The only way to cancel any low idle bounce is to add a grill guard(if possible) and front weights to cancel the delivered momentum at the flywheel at low idle due to the front engine mounts for the three cylinder engines.



leon

 

[KennyV]

Back to the OP initial question...
The more cylinders you have the smoother it will TEND to be....

This really is not of great importance to a tractor...


I have never thought my tractor (L4200) vibrated too much compared to a 5 or 6 cylinder.... If I go to idle with the AC and stereo on I'm not disappointed in the feel of things... KennyV

 

[LBrown59]

***there seems to be a lot of complaints about the Kubota B7800 and B3200 being vibrators when compared to 3 CYL versions of similar sized tractors. .

That's why I don't like the 4 cyl diesels.

Gas engines seem to do better with even numbers of cyls;while diesel engines appear to work better with odd numbers of cyls.

 

[ultrarunner]

Nothing like the old Buick Straight 8 for smoothness or a modern BMW straight 6...

 

[PHILIP8N]

That's why I don't like the 4 cyl diesels.

Gas engines seem to do better with even numbers of cyls;while diesel engines appear to work better with odd numbers of cyls.

The inline 6, gas or diesel, even number of cylinders, is about as closed to a natrually balanced engine you can ask for. 99.5% of all semi tractors use 6 cylinder inline diesel engines. Philip.

 

[KennyV]

Nothing like the old Buick Straight 8

Yeah.. I had a '48 ...great car. But I found the weak part of the engine... Babbitt bearings. KennyV

 

[rScotty]

Thanks for the replies, I was just wondering because I am looking at moving up in tractor size and all the JDs have 3 cyl and the Kubotas have 4 cylinders for about the same HP.

I design similar products and it often comes down to how much effort the manfacturer wants to put into smoothing out the inbalance - engine designers have no problem designing and balancing either number. Which is just another way of saying it's where designers decide to spend their money. For example, sleeved cylinder liners may cost more than directly bored blocks - but they also cool better so money can be saved in other areas. It's all trade offs. The cost of an additional cylinder's parts has to be considered against the cost of a driven balance shaft required by using a lesser number of cylinders. Often these basic decisions look more like politics than engineering.

I've got a three diesel tractors of 2, 3, and 4 cylinders.

The two cylinder is a low end direct injection Yanmar built to be absolutely bulletproof and cheap. It shakes. It has also not needed any maintenance in 30 years and still starts and runs same as it did when new.

The 4 cylinder is a new Kubota 60 hp turbo. I'd rate the engine construction as a good conservative motor design built with an eye on cost. It has some vibration, but not much or in any way objectional, but I notice I do tend to work at a RPM where it "feels" best.

The 3 cylinder is mid-30s HP non-turbo indirect injection type - also built by Yanmar. The quality of design and construction is obviously above the norm for tractors. It's also shows more thought in accessibility for routine maintenance. It is weirdly vibration free at all RPM - almost like an electric motor.

BTW, torque rules! Not HP, because HP is just torque times RPM. And unfortunately, engines are HP rated at full RPM...even though we tractor guys rarely run them that way. In fact, if torque is equal or close, a smaller motor can actually put out more HP by simply spinning it faster. Think about Torque first, then how RPM affects HP when comparing. High torque at low RPM also vibrates way less.
Enjoy! rScotty

 

[leonz]

So true , so true. I have the first 5 cylinder Isuzu Truck I have ever owned and its a great truck with the 5 banger Vortec -ithe 2008 is the last year that they contracted with GM to build trucks for them. I still have the 1995 4 by 4 (4 cylinder gas) that I bought new and it need frame work but is as good as new and I can still buy parts so its going back on the road this winter after the frame repairs.

 

[whistlepig]

I design similar products and it often comes down to how much effort the manfacturer wants to put into smoothing out the inbalance - engine designers have no problem designing and balancing either number. Which is just another way of saying it's where designers decide to spend their money. For example, sleeved cylinder liners may cost more than directly bored blocks - but they also cool better so money can be saved in other areas. It's all trade offs. The cost of an additional cylinder's parts has to be considered against the cost of a driven balance shaft required by using a lesser number of cylinders. Often these basic decisions look more like politics than engineering.

I've got a three diesel tractors of 2, 3, and 4 cylinders.

The two cylinder is a low end direct injection Yanmar built to be absolutely bulletproof and cheap. It shakes. It has also not needed any maintenance in 30 years and still starts and runs same as it did when new.

The 4 cylinder is a new Kubota 60 hp turbo. I'd rate the engine construction as a good conservative motor design built with an eye on cost. It has some vibration, but not much or in any way objectional, but I notice I do tend to work at a RPM where it "feels" best.

The 3 cylinder is mid-30s HP non-turbo indirect injection type - also built by Yanmar. The quality of design and construction is obviously above the norm for tractors. It's also shows more thought in accessibility for routine maintenance. It is weirdly vibration free at all RPM - almost like an electric motor.

BTW, torque rules! Not HP, because HP is just torque times RPM. And unfortunately, engines are HP rated at full RPM...even though we tractor guys rarely run them that way. In fact, if torque is equal or close, a smaller motor can actually put out more HP by simply spinning it faster. Think about Torque first, then how RPM affects HP when comparing. High torque at low RPM also vibrates way less.
Enjoy! rScotty

It's not that simple. Torque does not always rule. Torque is best for motors that pull loads and do work. At the drag strip horsepower will win the race.

 

[easygo]

Yeah you are right. But if I remember correctly the OP was looking to upgrade his/her tractor not a dragster.

This is a very informative thread. I'm lovin' it.